This CKA practice question tests your understanding of troubleshooting. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A Service of type ClusterIP is not reachable from within the cluster. Pods backing the Service are running and healthy. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
DNS resolution failure
Why wrong: DNS resolves Service name to ClusterIP; connectivity fails after.
Ingress controller not set up
Why wrong: Ingress is for external; ClusterIP is internal.
Service type should be NodePort
Why wrong: ClusterIP works internally.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
kube-proxy not running or misconfigured
When Pods are healthy but a ClusterIP Service is unreachable from within the cluster, the most common cause is that kube-proxy is not running or is misconfigured. kube-proxy is responsible for implementing the ClusterIP virtual IP by programming iptables (or IPVS) rules on each node to forward traffic to the selected Pods. Without these rules, packets destined for the ClusterIP are dropped or rejected, even though the Service and Endpoints objects exist.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
DNS resolution failure
Why it's wrong here
DNS resolves Service name to ClusterIP; connectivity fails after.
Ingress controller not set up
Why it's wrong here
Ingress is for external; ClusterIP is internal.
Service type should be NodePort
Why it's wrong here
ClusterIP works internally.
Option-by-option analysis
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The CKA exam frequently reuses these exact scenarios with slightly different constraints.
Why this is wrong here
DNS resolves Service name to ClusterIP; connectivity fails after.
Why this is wrong here
Ingress is for external; ClusterIP is internal.
Why this is wrong here
ClusterIP works internally.
Analysis generated from the official CKAblueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
The trap here is that candidates often assume a healthy Pod and Service object guarantee connectivity, overlooking that kube-proxy must actively program the underlying network rules to make the ClusterIP routable.
Detailed technical explanation
kube-proxy watches the Kubernetes API server for Service and Endpoint changes and updates iptables rules in the NAT table (e.g., KUBE-SERVICES chain) to redirect traffic from the ClusterIP to a randomly selected healthy Pod IP. If kube-proxy is not running, these rules are absent, and the kernel drops packets to the ClusterIP because no local process is listening on that virtual IP. A common real-world scenario is a node reboot where kube-proxy fails to restart due to a misconfigured DaemonSet or missing binary.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the CKA exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Troubleshooting — This question tests Troubleshooting — Read the scenario before looking for a memorised answer..
The correct answer is: kube-proxy not running or misconfigured — When Pods are healthy but a ClusterIP Service is unreachable from within the cluster, the most common cause is that kube-proxy is not running or is misconfigured. kube-proxy is responsible for implementing the ClusterIP virtual IP by programming iptables (or IPVS) rules on each node to forward traffic to the selected Pods. Without these rules, packets destined for the ClusterIP are dropped or rejected, even though the Service and Endpoints objects exist.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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